Ever since the golf industry has shifted away from persimmon wood type golf clubs into the modern metal wood type golf clubs, golf club engineers have always tinkered with the weight distribution of the golf club head in order to improve the performance of the golf club head. Because the modern day metal wood golf clubs are generally made out of a lightweight titanium type of material, they may not be able to shift a significant amount of weight around the golf club head. In order to address the weighting deficiencies of titanium, golf club engineers have attempted to attach higher density metallic materials to the body of the titanium golf club head.
U.S. Pat. No. 4,824,110 to Kobayashi shows one of the earlier attempts at combining different materials having different specific gravity to form a golf club head in order to adjust the weighting distribution of the golf club head. Moreover, U.S. Pat. No. 4,824,110 focuses on the usage of fiber reinforced plastic as the lightweight material while using traditional titanium or steel as the heavy weighted material. Although the usage of fiber reinforced plastic is one way to achieve significant discretionary weight within a golf club head, it does so at the expense of some other performance characteristics such as the sound of the golf club at impact.
Despite all of the design advantages associated with the fiber reinforced plastic, the usage of completely metallic golf club head is still preferred by much of the golfing public for its superior sound characteristics. The problem with the titanium material used to create a metal wood type golf club head is that it may not always join well together with materials such as tungsten, molybdenum, or zirconium; all of which have a higher density than titanium. U.S. Pat. No. 5,935,019 to Yamamoto recognizes this issue and identifies this issue by saying that “it is difficult to weld together metals of different types, and especially difficult when one of the metals is titanium or a titanium alloy.” U.S. Pat. No. 5,935,019 addresses this bonding issue by forming a metallic hollow golf club head with a sole plate molded form a light metal and formed with a fitting hole, and a weighted structure comprising a weight of a heavy metal press-fitted into a ring-shaped spacer formed of the same light metal as the sole plate, said weighted structure being fitting into the fitting hole, and the ring-shaped spacer and the sole plate being welded together.
U.S. Pat. No. 6,379,265 to Hirakawa et al. illustrates another attempt to joint two metallic materials together in a golf club head to improve the performance. More specifically, U.S. Pat. No. 6,379,265 illustrates a metal wood club including a sole plate and a weight body which is fastened to this sole plate via a spacer. A recess which accommodates the spacer and weight body is formed in a portion of the sole plate, and undercut part is formed in the inside circumferential portion of the recess, and a circumferential groove is formed in the outer circumferential portion of the weight body. When the weight body is press-fitted in the recess with the spacer in between, the spacer is forcibly engaged with the undercut part and circumferential groove, thus allowing the weight body to be firmly fastened to the recess of the sole plate of the club head.
Despite all of the attempts to attach high density weights to a metallic golf club head, most of these attempts utilize crude press-fitting techniques that do not allow the materials to bond together in a clean fashion. Moreover, the press-fitting techniques discussed above do not help limit the relative rotation of the heavy density weight with respect to the golf club head, which could lead to undesirable rattling. Hence, it can be seen from above there is a need in the field for a golf club head that is capable of joining together a heavy density metallic material together with a lower density metallic material in a manner that not only provides a clean and aesthetically pleasing joint, but also in a way that prohibits the rotation and vibration of the weight itself.